The present invention relates to a pneumatic tire which includes a plurality of sipeings provided side-by-side in a block, and which can be employed as a studless tire suitable for running on an ice and snow road surface.
In the pneumatic tire, in order to enhance the running performance on an ice and snow road surface, a block provided in a tread portion is formed with a large number of sipeings. By increasing a road surface scratching force (edge effect) obtained by the edge of the sipeing, the driving force and braking force on the ice and snow road are secured. If the number of sipeings is increased, however, the degree of falling down of becomes large. As a result, if the edge effect does not function effectively, and the running performance on the ice road is deteriorated.
Thereupon, to prevent the block from excessively fall, a zigzag type sipeing structure as shown in FIG. 9, is proposed in Japanese published patent application 2003-25812.
In this sipeing structure, its wall surface configuration of sipeing is a kind of so called MIURA-ori structure (MIURA folding manner). In the MIURA-ori structure, an opening edge shape b of the sipeing a which opens at a block surface has a zigzag portion b1. From the block surface toward the sipeing bottom, the zigzag portion b1 is displaced toward one side and the other side by turns in a longitudinal direction of the sipeing while maintaining the zigzag shape. Such a sipeing a forms a three dimensional concavo-convex 3D crooked curved surface comprising parallelograms. With this, concavo portions and convex portions of opposed wall surfaces of the sipeing a mesh each other so that it is possible to effectively prevent the block from falling.
Further, the sipeing a has the same zigzag shape in each depth position, a sipeing forming knife blade in a tire vulcanization mold can be pulled out from the tire easily, and it is possible to suppress the producing efficiency of the tire, and to suppress damage such as bending of the knife blade.